It is well known to use fibre-reinforced resin composite materials for the manufacture of structural components in a variety of industrial sectors. For some applications, the fibre-reinforced resin composite materials are manufactured from what are known in the art as prepregs—a prepreg comprises fibrous material pre-impregnated with a resin, and the amount of resin is matched to the amount of fibre so that after plural prepregs have been laid up into a mould and the resin has cured, optionally with a preliminary full wetting out of the fibrous material by the resin if the prepreg was initially not fully impregnated, a unitary fibre-reinforced composite material moulding is formed with the correct ratio of fibre to resin so that the material has the required material properties.
When a composite material is used for interior panel construction for mass transport applications, such as aerospace, trains, ferries, etc., in particular for the interiors of such vehicles, a fire, smoke and toxicity requirement is necessary. Historically, composite materials such as phenolic, cyanate-ester, sheet moulding compound (SMC), modified vinyl-ester and halogenated epoxides have been used for these applications. They all have significant disadvantages as shown in the table below:
TABLE 1Known Material Comparison TableFire-SmokeSmokeMechanicalEase ofHealth &FamilyretardancyDensityToxicityPropertiesprocessingSafetyCostSheetPoorPoorPoorPoorGoodTBCLowMouldingCompound(SMC)ModifiedPoorPoorPoorPoorPoorPoorLowvinyl-esterHalogenatedGoodPoorPoorExcellentExcellentPoorMediumEpoxidesPhenolicExcellentExcellentExcellentPoorPoorPoorLow/ResolesMediumCyanateGoodGoodExcellentGoodGoodGoodExpensiveEsters
Prepregs employing a phenolic-based resin have been historically used for interior panels in aerospace and mass transit applications for many decades. Although such phenolic resins offer excellent fire, smoke and toxicity (“FST”) properties, there is an industry desire to seek replacement resin materials for such prepregs which offer improved health and safety performance, and lower-cost processing, than phenolic resins.
Phenolic resins for use in such prepregs are cured using a condensation reaction which releases volatiles and water during curing. This requires the use of press-curing under an imposed pressure in order to impart high pressures (6 bar) to reduce the expansion of large voids within the laminate during curing of the resin. Such voids would otherwise decrease the mechanical properties of the laminate. This press-curing increases processing cost. Secondly, the release of volatiles creates poor surface finishes that require significant filling and fairing of the cured components at a substantial additional cost. The release of volatile components, and solvents, also results in the need to take specific health and safety precautions when using such phenolic resins.
Offshore oil and gas rigs have requirements to install lightweight blast protection panels. These are typically composite sandwich panels. Known phenolic prepregs are often used in these applications. However; they are limited in their application in primary structures due to their poor relative toughness and strength properties.
The use of composite materials in civil construction offers greater freedom as to the structures which can be constructed. Larger, more complex shapes which are not possible with traditional construction materials are easily formed with composite materials. Due to composites poor relative fire, smoke and toxicity properties compared to materials such as concrete and steel, the use of composites in these applications is limited. Phenolic composite panels may be used; however, they suffer from poor mechanical properties which limit their use in primary structures.
Addition-cured epoxide resins are well known in the composites industry to offer excellent mechanical properties and good health and safety properties. They are however, intrinsically flammable materials and, when used unmodified, are not suitable for applications where fire, smoke and toxicity properties are required. This has mitigated against their use in the aerospace industry, particularly for interior components
Epoxides have commonly been modified with halogens (such as bromine and chlorine) in order to impart fire-retardant properties to the cured matrix. The two main disadvantages to this approach are high toxicity of smoke during combustion and poor health and safety characteristics associated with the material in both the uncured and cured state.